Distillation of fatty acids



April 23, 1935. .L. M. TOLMAN mswnmmon OF FATTY ACIDS 2 Sheets-Sheet 1 Filed Dec. 1, 1932 A ril 23,1935.

L. M. TOLMAN DISTILLATION ,OF FATTY ACIDS 2 Sheets-Sheet 2 Filed Dec. 1, 1932 Patented Apr. 23, 1935.

UNITED STATES PATIENT OFFICE masses;

Lucius M. Tolman, Chicago, 111., assignor to New Process Fat Refining Corporation, Chicago, 111., a corporation of Delaware Application December 1, 1932, Serial No. 645,289 2 Claims. (01. 202-53) The present invention relates to improvements in-the distillation of fatty acids or of mixtures containing the sam together with fats or unsaponifiable matter, and will be fully understood 5 from the following description illustrated by the accompanying drawings, in which apparatus suitable for carrying out the invention is diagrammatically illustrated.

In the distillation of fatty acids or mixtures containing them in order to recover the fatty acids as distillates, as hitherto conducted, there are serious losses in the proportions of the fatty acids recovered, and-a marked degradation of the undistilled residue. In general, in order to secure a high grade fatty acid product, it has been necessary to redistill the fatty acids recovered in such an operation, this redistillation being accompanied by a further loss. Such losses in the distillation operation and degradation of the products have persisted, notwithstanding the development of the use of high vacuum in the operation.

By operating in accordance with the present invention, it has been found possible to prevent the losses and avoid the deterioration of the products in the processes as hitherto conducted, thereby making it possible to dispense with further distillation of the fatty acid product while at the same time greatly improving the economy and efficiency of the distillation operation.

It has been discovered that a large part of the difllculty is due not only to an excessive time of heating, but to entrainment of particles of the undistilled residue in the distillate. This difficulty has been in large part overcome and a distillate of higher purity and color obtained both by carefully controlling vapor velocity of the distillate and by careful removal of entrained matter.

In order that the invention may be fully understood, it will be described in connection with the treatment of a suitable fatty acid stock, for example, the mixture derived by splitting the fats of a commercial grease or oil by any suitable process, such as the Twitchell process. Such a mixture, in ordinary practice, may contain 92 to 95% free fatty acids. When subjected to high vacuum distillation according to the processes hitherto in use, the yield of fatty acid distillate in the first distillation is in the order of 85%, and on redistillation, the yieldis in the order of 76% 50 of the original stock.

The apparatus used is illustrated in the drawings, wherein Fig. 1 shows a broken diagrammatic.

view partially in section of the distilling apparatus; Fig. 2 is a broken sectional front elevation 55 of the distilling tower; Fig.3 is a detail plan view residue.

dency toward entrainment is very pronounced.

of one of the screenbaflles of the tower; and Fig. 4 is a detail plan viewof one of the disk baffle plates of the tower.

In'eflecting distillation in accordance with the present process, the stock to be distilled isfed 5 from a suitable source under pressure, for example, by a pump, (not shown) through line 5 into a pipe heater 6, which is heated in any suitable manner. In the form illustrated, the pipe heater 6 is shown as a coilin a lead bath I in a 10 retort 8, heated in any suitable manner, as by the gas heater 9. In passing through the pipe heater 8, the oil is heated to a vaporizing temperature, ordinarily 400 F. or higher, say from 450 F. to 600 F., (the temperature employed depending 15 in part on the vacuum employed. in vaporization). While being heated the oil is preferably maintained under pressure at the outlet of the coil, to avoid any substantial or excessive volatilization of fatty acids in the coil. In general, the coil out- 20 let temperature shouldnot exceed 650 F. The pressure maintained at the outlet of the coil, as shown by the gauge llLmay suitably be about 20 lbs. per square inch or higher, say 40 to 60 lbs., although much less pressure will suffice to prevent substantial volatilization. At relatively low temperatures only enough pressure, if any, need be used to regulate the flow After leaving the coil 6, the heated stock passes through a pipe II to a manifold [2, from w ch 30 it may be discharged through either of lines I3, M or I5 into the tower IS. The lines l3, l4 and 15 are provided with pressure release and control valves ll, I8 and I9 respectively, to permit the desired reduction in pressure on the stock as it enters the tower.

The tower I6 is provided internally with baflles or distributors 20 and 2|. The baflle plates 20 may suitably be screen plates of the diameter of the tower and the baffle plates 2| disk plates of smaller diameter. The form of the bailie plate is of particular importance because the fatty acids have a remarkable tendency toward entrainment of the dark-colored portions of the undi'stilled Even with low vapor velocities, which should not be materially over 4 feet per second at a high vacuum, and are preferably in the neighborhood of 2 or 3 feet per second, the ten- The higher the vacuum, the greateris the permissible vapor velocity. At a 21-22" vacuum, a velocity of 2 to 2 /2 feet per second is satisfactory, but even then only if proper entrainment-breaking means are provided.

The type of entrainment-breaking means used will of course vary with the size of the still and other factors. By means of the present invention, however, distillate having a color on the N. P. A. scale of 3 or better may be produced on the first distillation. The following example gives a type which has proved exceptionally satisfactory, namely, such type as illustrated in Figs. 2-4 of the drawings. In thedrawingsthe tower l6 is preferably 30 inches in height (excluding the rounded ends) and of 6 inches internal diameter. The plate 22 is placed 4 above the bottom edge of the tower. Five inches above this is placed the baflie 2|0. This baffie is a. plate 4%" in diameter and having three holes A-inch" in diameter placed 1%" from the edge ofthe plate. The structure of the baffle is shown in Fig. 4.

Five and one-fourth'inches above the baflle M is placed a screen baflle 200, which is the full diameter of the tower. As shown in'Fig. 3, the screen baffle has a 1%" hole at its center and three holes in diameter placed from the edge of the plate.

Six inches above baiile-200 isQ another-"plate inches above baiile 2H--is a'noth tical with 200.

In this construction the upperii'inlet;: l3 f n diameter of A", and is two inchesfb'elow{the bafilex200. The steam inlet 24 is a t pipe, perforated on its lower side with smallopenings;

through which the steam enters in a downward The heated fatty acid-containing'sto the tower through either line I 3," preferably through an upper'line l3 or lilf discharged thereinto at reduced pressure. The tower is maintained under substantial :vacuum; preferably 20-22 inches or higher, as hereinafter more fully set .forth. It descends the tower, meeting the superheated steam discharged into the towe from the distributor 24, acid vapors rise to the top of thetower pass out through the vapor line 26170. denser 21. may be ,variedin accordance with the'vac uum employed and the proportion of fatty acids pres ent in the stock. Thus, with a stock with the character hereinbefore referred to, and with the vacuum in the tower of about 22 inches, the proportion of steam to fatty acid may be approximately 40 to 60. It will be readily understood that with higher vacuum, less steam may be employed and also that the proportion of steam may be varied in accordance with the temperatures of operation and the nature of the fatty acids present. The outlet temperature at the top of the tower may vary from 375 to 550 F. with a vacuum of 22 inches, and with higher vacuum lower outlet temperatures may, of.course, be employed; for example as low as 350 F.

The undistilled residue discharges continuously through the trapped outlet pipe 23 into the lower portion of the tower I6 below the partition ioperated' by heating 1.5:: gallons proximately 500 and..the-fatty' H Q The proportion of stea'mfsupplied plate 22, from which it may be withdrawn through the valved discharge line 28 into the container 29. When the latter is filled, the residue may be diverted to a second, similar container (not shown) while the first residue container is vented to the atmosphere and its contents removed.

The fatty acid containing vapors discharged from the tower l6 through the vapor line 26 are condensed to liquids in the condenser 21 and discharged through manifold 30 and lines 2| and 32 to one of the receivers 33 or 34 respectively. These receivers are employed alternatively, the

one in use being disconnected from the system when it isfilled' and the other being then connected to the system. Each of the receivers 33 and 34 is connected by a valved line 35 and 36 respectively, to the vacuum manifold 31, which is connected to a suitable vacuum pump by which the desired vacuum is maintained upon the system, and uncondensed with vapor. It will be understood that the lines through which the heated stock passes from the heating coil to the tower, the tower itself and the lines leading therefrom, may be lagged or heat insulated.

:By-operating in the manner above set forth,

from the stock hereinbefore described, it has been possible to produce in continuous operation a Ifatty acid distillate product with a yield of 92% (on the original stock) of a quality superior to ,that' obtained in the second distillation in the processes as hitherto conducted. The'fatty acid distillate is produced continuously of uniform quality and any portion thereof maybe segregated and pressed, the admixture of earlier and later distilled portions to secure a pressable product not beinggnecessary as in prior operations. At the same time, the residue of the distillation process is of an entirely different character from -the. "pitch obtained inprior distillation processes and. the saponiflable constituents thereof may be recovered in a further distillation process.

example, the tower shown in Figs. 2-4 was of tallow grease per hour-at; a coil temperature of 600-630 F.,

and injecting 11.5 pounds of steam per hour into I the tower- 5al\t' a pressure of 60-80 pounds and a temperature of 725-750 'F. The tower was held under a 21', vacuum, and a temperature of 'apwas maintained at the top of the tower. Distillate was obtained at the rate of 10.4 pounds per hour, having the remarkably good color 01 2 on the N. P. A. scale. The N. P. A. scale is thecolor scale of the National Petroleum Association, and is well known to those skilled in the art.

responding greases, even with a subsequent chemical decolorizing treatment. At the same time the yield produced was 87.1% on the basis of the stock introduced, and approximately 92% on the acid content thereof. An analysis of the stock, bottoms and distillate was as follows:

Total Free fatty acid (molelc) gig Crudeacid-.. -Q 39.1 aazs 211 Distlllate 4oz. 101111 2.50 Bottoms. 51.11 sac 83.9

} This color is much better than is ordi-' narily secured by double distillation of the cor- 1,eea,eos

For example by operating at a tower temperature of 450 F., in a vacuum of 29", and feeding 2.15 gallons of tallow grease acids per hour, a color of 2 N. P. A. is obtained. In this instance, however, a yield of 92.6% on the original stock was obtained, as contrasted with 87.1% in the preceding example. The velocity in the last case was considerably higher than 2.15, but considerably less steam was used and the vacuum was higher.

In the production of distillate of good color, it is particularly important that the undistilled residue be continuously removed from the tower. It has been discovered that if bottoms are allowed to accumulate in the tower, the color of the distillate rapidly becomes worse.

In the construction of the apparatus, it is found that ferrous or predominantly ferrous metals may not be employed in the construction of the pipe coil and the distillation tower, as they are rapidly corroded. I have found that nickel or predominantly nickeliferous alloys, such as Monel metal, may besatisfactorily employed for the pipe heater 6 and the lines I I, II, It, It and I! through which the hot fatty acid-containing stock is conveyed to the tower. Either nickel or copper may be employed in the construction of the tower. By the use of a heating coil and transfer lines of copper or ofnickel or nickeliferous material I have found that the desired heating of the material may be affected without corrosion and without contamination of the distillate or residual products.

It is readily apparent that the process of the present invention may be employed under circumstances in which the proportions of fatty acids present differ widely from those in the specific example set forth above; for example, in the separation of small proportions of free fatty acids from fats or oils in the production of refined or neutral fats or oils and in deodorizing fats and oils.

This application is a continuation-in-part of my copending application Ser. No. 484,895, filed September 27, 1930,

WhatIclaimasnew anddesiretosecureby Letters Patent is: 4

1. The method of distilling a fatty acid containing stock to remove fatty acids therefrom which comprises passing a restricted stream of the stock through a confined e in a heating zone in which it is brought to a temperature of about 600 1'. while maintaining at least 20 lbs. super-atmospheric pressure thereupon, discharging the heated stock into a tower, maintaining a vacuum of at least 20 inches Hg in said tower, and removing volatilised fatty acids therefrom.

2. The method of distilling a fatty acid-containing stock to remove fatty acids therefrom which comprises: passing a restricted stream of the stock through a confined passage in a heating zone in which it is brought to a temperature of about 600 F. while maintaining at least 20 7 lbs, super-atmospheric pressure thereupon, discharging the heated stock into a tower, maintaining a vacuum of at least 20 inches Hg in said tower, introducing superheated steam in said tower to pass therethrough countercurrent to the heated stock, maintaining an outlet temperature in said tower of about 400 F., and removing voiatilized fatty acids therefrom.

LUCIUS M. TOLMAN. 

